The invention relates to a directional high-frequency broadband transformer or antenna coupler in the form of a printed circuit including an inductance component provided with a magnetically closed ferrite core and conductive webs printed on an insulating support and a capacitance component in the form of a conductive layer.
A high frequency transformer arrangement without ferromagnetic material for the meter and decimeter wave lengths is known from the German publication DE-AS No. 1073046. This known device is provided with inductances having a defined configuration and with capacitors which are shaped as a double sided printed circuit. The spiral like inductances consist of two coils which are connected with each other on each side of a substrate support. The capacitances are formed as oppositely disposed conductive layers which are separated by the substrate and are galvanically contacted, whereby the contacts interconnect the layers and the coil connections.
A further known transformer in accordance with DE-AS No. 2230587 in the printed technology has a platelet like winding support made from electrically insulating material with at least a planar spiral like winding mounted thereon, and a ferrite core whose magnetic circuit is coupled with the electric circuit of the winding(s). The ferrite core is separated into two parts, i.e., it has an air gap in the magnetic circuit. No sufficient high inductances can be obtained therewith at high frequencies in the megahertz range, since ferrite materials have a low permeability at these frequencies.
Furthermore, known are coil devices with a multi-hole core, wherein two pairs of coils are mounted on an insulating support and are in the form of printed conductive webs. The insulating support is provided with openings arranged within and/or outside the coils. These openings are filled with non-sintered ferrite material and ferrite material is also applied on the upper and lower side of the insulating support.
Subsequently the entire device is sintered, so that a coil arrangement with closed ferrite core is obtained which has a very low magnetic stray flux (DE-OS No. 2917388). However, the technology which is used for making the ferrite cores is rather expensive and can only be controlled with difficulties, i.e., the transmission characteristic of the coil arrangement have large deviations in mass production.
Finally, it is known from DE-OS No. 2830732 to reduce parasitic capacities in coils with printed conductive webs and to increase the limit frequency of the coil by making the insulating distance between the conductive webs non-constant, at least in partial ranges. However, no closed magnetic circuit can be obtained, as required for wide band transformers.